It is an object of this invention to provide fabrics for decorative and functional purposes, unlike the engineering fabrics mentioned above. Thus, a woven fabric of the instant invention contains a plurality of large diameter, low modulus filaments or fibers in yarn form, this yarn being used for warp and/or fill yarns.
In order to produce a soft hand and acceptable drape for decorative functional uses such as drapes, curtains, wall coverings, seat covers, table cloths, etc., the fibers utilized in the invention have an unusually low modulus of elasticity (E.sub.f) relative to conventional fibers. The range of the modulus of elasticity of the fibers is from 2,000 to80,000 pounds/inch.sup.2 (p.s.i.). Such fibers, with moments of inertia of from 400.times.10.sup.-14 in..sup.4 to 7.8.times.10.sup.-9 in..sup.4, will have a stiffness parameter, as defined below, in the range of 8.0.times.10.sup.-9 to 62.4.times.10.sup.-5 p.s.i. Thus, in spite of the large dimensions of the cross-sections of the fibers, they still remain flexible and supple because of their extremely low values of elastic modulus compared to conventional fibers.
By "large diameter fibers" is meant fibers of any synthetic polymer having a diameter in a range of from about 0.003 to 0.020 in., preferably from about 0.006 to about 0.015 in. These fibers usually have a denier of from 25 to 500 for fibers made of material having a specific gravity in the range of from about 0.90 to about 1.4. The modulus of elasticity (E.sub.f) is determined by measuring the initial slope of the stress-strain curve derived according to the American Society for Testing Materials Manual, Standard Method No. D2256-69. Strain measurements are corrected for gauge length variations by the method described in an article. entitled "A Method for Determining Tensile Strains and Elastic Modulus of Metallic Elements," American Society for Testing Materials Transactions Quarterly, 60(4):726-727 (1967).
By "a fiber having a low modulus of elasticity" is meant a fiber with a modulus of elasticity of from about 2,000 to about 80,000 p.s.i.
Under normal loading conditions, fibers bend about a neutral axis where the moment of inertia will be a minimum value. The moment of inertia (I.sub.f) about this neutral axis is calculated using the following equation: EQU I.sub.f =.intg.y.sup.2 dA
where dA is any incremental area of the fiber cross-section and y is the distance any such incremental area is from the neutral axis. The above equation illustrates that the moment of inertia of the fiber is a function of the cross-sectional configuration of the fiber. Thus, the hand of a fiber may be altered by changing its cross-sectional configuration. Specific examples of fibers having different cross-sectional configurations and the specific equations for calculating the moments of inertia for such fibers are given in a paper presented at the 47th Annual Meeting of the American Society for Testing Materials, and published in Vol. 44 (1944). For example, for a circular cross-section ##EQU1## wherein d is the fiber diameter.
The cross-sectional configuration of the fiber is not critical so long as the moment of inertia falls within the range of from about 400.times.10.sup.-14 in..sup.4 to about 7.8.times.10.sup.-9 in..sup.4. However, the fibers preferably have a generally circular cross-section. Such a fiber would have to have a diameter in a range of from 0.003 in. to about 0.020 in. in order to have the required moment of inertia.
The fiber stiffness is a function of the material properties of the fiber, the geometry of the fiber, and the manner in which load is applied to the fiber. In general terms, one may compare the hand of different fibers by comparing the stiffness parameter of the fibers, where each fiber has a uniform cross-section and is composed of the same material throughout. This stiffness parameter (K.sub.f) is the product of the elastic modulus (E.sub.f) of the fiber and the area moment of inertia (I.sub.f) of the fiber: EQU K.sub.f =E.sub.f .times.I.sub.f.
Because of the extremely large cross-section of the fibers utilized in the invention, yarn made from them will contain fewer fibers per bundle than conventional yarns. For example, a 1000 den. yarn made of 5 denier (den.) nylon filaments or fibers (5 den. is equivalent to a 0.001 in. diameter circular nylon fiber) will have 1000/5, or 200 filaments or fibers. A 1000 den. yarn made of 100 den. filaments or fibers of the invention will have 1000/100, or 10, filaments or fibers.
Fabrics made from yarns with low modulus, large diameter fibers could be as flexible as those made with conventional nylon, polyester, acrylic, cotton, wool or blended yarns. The stiffness of a yarn is approximately given by the following equation: EQU S=n.multidot.E.sub.I f.multidot.I.sub.f
where n=number of filaments in the yarn PA1 E.sub.f =modulus of elasticity (of the fiber in p.s.i.) PA1 I.sub.f =moment of inertia (of fiber cross-section in in.)
The stiffness of a fabric of a given construction, i.e., a given number of warp and filling yarns per unit area, is related directly to the yarn stiffness. For similar woven constructions, the stiffness of a fabric made of yarns with low modulus, large diameter fibers (A) can approximate that of a conventional fabric (B) if the yarn stiffnesses are made equal: EQU (nE.sub.f I.sub.f).sub.A =(nE.sub.f I.sub.f).sub.B
For example, for yarns of equivalent denier, ##EQU2## and if (dn.sub.f).sub.A =100, (dn.sub.f).sub.B =5, and (dn.sub.y).sub.A =(dn.sub.y).sub.B =1000, then EQU (10E.sub.f .multidot.I.sub.f).sub.A=( 200E.sub.f .multidot.I.sub.f).sub.B
Now, if (I.sub.f).sub.A =3.068.times.10.sup.-11 in..sup.4, (I.sub.f).sub.B =4.9.times.10.sup.-14 in..sup.4 and (E.sub.f).sub.B =500,000 p.s.i., then the value of (E.sub.f).sub.A required for equivalent yarn stiffness is ##EQU3## This falls within the elastic modulus range for fibers utilized in the invention (2,000 to 80,000 p.s.i.).